1. Technical Field
The present disclosure relates to a bi-directional converter, a controller, and a semiconductor device, and, in particular, to a technology of preventing a switching element in a bi-directional converter from turning on unintendedly.
2. Description of the Related Art
Switching converters, which step up a voltage supplied from a power supply and supply the increased voltage to a load, are put in practical use.
In the case where the load that receives supply of the voltage from the switching converter is a device which converts electrical energy into kinetic energy, the load may generate a voltage that is greater than the supplied voltage, due to counter electromotive force. For example, in vehicle applications, solenoids and motors that drive, for example, a fuel injector, various solenoid valves, and a power steering are one example of the load that can generate a high voltage due to counter electromotive force.
Power regeneration in which a high voltage generated at a load is stepped down and collected as electrical power to be used by the power supply (for example, in-vehicle battery), is an important technology of enhancing the efficiency of the power supply utilization. A bi-directional converter which allows both a step-up operation from a power supply to a load and a step-down operation from the load to the power supply can be configured of a switching converter (for example, Japanese Unexamined Patent Application Publication No. 2007-60853, PTL 1), for example.
By the way, a phenomenon what is called self turn-on is known to occur in a power conversion circuit such as a switching converter and an inverter which include switching elements. The self turn-on refers to a phenomenon, in the power conversion circuit, that one switching element that should be kept off turns on unintendedly due to fluctuation of control voltage for the switching element when another switching element is about to turn on. The self turn-on can be a cause of malfunction such as short circuiting of the power supply, for example.
Several countermeasures for avoiding the self turn-on are well-known (for example, Japanese Unexamined Patent Application Publication No. 2000-59189, PTL 2).
PTL 2 discloses a gate circuit which is applied to an inverter. The gate circuit connects a negative bias voltage source that is for off-control and a gate terminal of a switching element via a variable resistor, wherein the variable resistor changes to a small value (for example, to substantially zero resistance) at a predetermined time while the switching element is turning off.
According to the gate circuit, the effects of negative bias increases after a delay that is defined by the predetermined time after the switching element turns off, and the off-state of the switching element is thereby stabilized. Accordingly, the switching element is inhibited from turning on unintendedly after the delay, and a transient gate current is inhibited as well from flowing through the switching element immediately after the switching element turns off.
Thus, the bi-directional converter disclosed in PTL 1 and the gate circuit disclosed in PTL 2, in combination, may achieve a bi-directional converter which yields a certain effect to prevent the switching element from turning on unintendedly.